One in business making outburst (6)
I believe the answer is:
tirade
'outburst' is the definition.
(I've seen this before)
'one in business' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'business' becomes 'trade' (trade is a kind of business).
'i' going inside 'trade' is 'TIRADE'.
'making' acts as a link.
(Other definitions for tirade that I've seen before include "Intemperate outburst" , "Verbal broadside" , "A prolonged rant or harangue" , "strong words" , "Prolonged speech of abuse" .)